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remote sensing > quiz 2 > Flashcards

quiz 2 Flashcards

1
Q

what are the two types of coordinate systems

A
  • Cartesian coordinate system
  • Polar coordinate system
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2
Q

what is a map projection and what are the two elements of map projections

A

Project a round globe onto a flat surface
1.) projective surface
2.)perspective point

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3
Q

what are the three map projection surfaces

A

1.)Cylindrical
2.)Conical
3.)Planar

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4
Q

What are the three map projection viewpoints

A

Gnomonic – Earth center
Stereographic – Earth Surface
Orthographic – infinity

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5
Q

where is the view point on a gnomonic viewpoint

A

Earth center

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6
Q

where is the view point on a Stereographic viewpoint

A

Earth Surface

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7
Q

where is the view point on a Orthographic viewpoint

A

infinity

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8
Q

What are the four properties of map projection and how many can be kept

A

you can only keep 2 and the four properties are
– Area (equal-area or equivalent)
– Shape (conformal or orthomorphic)
– Distance (equidistant)
– Direction (azimuthal or zenithal)

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9
Q

What is preserved and not in a cylindrical projections

A

Shapes are preserved
But not area or bearings or distances

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10
Q

what type of projection is mercator

A

cylindrical

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11
Q

what are conic projections best for

A

Best for hemispheres
or small regions

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12
Q

what type of projection is lamber

A

conic

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13
Q

what distortions does conic projection have and what does it keep

A

Distortions
–Distance?
* Yes
–Areas?
* No
–Bearings?
* Yes

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14
Q

what are planar projections good for

A

Good for one hemisphere

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15
Q

what are the types of planar projections?

A
  • Gnomonic projection
  • Stereographic projection
  • Orthographic projection
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16
Q

what are the distortions and what is kept on a planar projection

A
  • Distortions
    –Distance?
  • Yes
    –Areas?
  • Yes
    –Bearings?
  • No
17
Q

what are the pros and cons of UTM

A
  • Advantage
    – Minimal Distortion
  • Disadvantage
    – Multiple zones
18
Q

what is a datum

A

Datum - formal description of the Earth surface

19
Q

what is a geodetic datum and what are its two parts

A
  • Geodetic datum - reference system describing
    Earth’s surface.
  • Geodetic datum contains two parts:
    – Shape of the Earth: ellipsoid (geoid)
    – Reference points and axis against which
    measurements are made
20
Q

what is nad 83

A
  • North America Datum - NAD 83
    – Replaces NAD 27 datum
  • Initial point in Kansas: Meades Ranch Station
    – Based on ellipsoid
    – Geocentric
    – Suited for the entire planet
21
Q

what is WGS 84

A
  • World Geodetic System 84 - WGS 84
    – Standard use in cartography, geodesy, and GPS
    – Based on the same ellipsoid as NAD83 (GRS80)
    – Coordinate system origin: Earth’s center of mass
22
Q

What are the segments of GPS

A

1.)control
2.)Space
3.)User

23
Q

How many satellites do we need for GPS

A

four for trilateration

24
Q

what are the 5 GPS errors

A
  • The errors experienced by the GPS users:
    1. Satellite clock-they are not perfect
    2. Satellite orbit-
    3. Atmospheric delays
    4. Multipath-Signal delay due to scattering off objects on earth
    5. Receiver clock
25
Q

What is a PDOP?

A

Position Dilution of Precision- basically the further spread out satellites are the better your location will be

26
Q

How can we improve the accuracy of our GPS measurements? 3 ways

A
  1. Solution wait for better acquisition (not very practicable)
  2. Solution: Differential GPS (DGPS)
    Post processing of location using GPS
    3.)Real Time Kinematics GPS:Measure the phase of the signal’s carrier wave in addition to other information
27
Q

what are the pros of aerial photography

A

Advantages
– Improved vantage point
– Capability to stop action
– Permanent recording
– Broader spectral sensitivity
– Increased spatial resolution
– Increased geometric fidelity

28
Q

what is focus and what does it depend on

A
  • The process of adjusting the lens to achieve
    maximum sharpness to the chosen subject
  • Focus depends on:
    1. Focal length of the lens, f
    distance from lens at which parallel light rays are focused to a point
    2. Distance between lens and object, o
    3. Distance between lens and image plane, i
29
Q

what is f-stop

A

f-stop - diameter of the lens opening of a camera
f-stop number increases = diameter of the lens opening decreases→ image exposure decreases

30
Q

what are the advantages of digital images

A

Enhanced image capture capabilities
– sensitivity (response to reduce amount of radiation)
– linearity (response to amount of radiation)
– dynamic range (difference between darkest & lightest)
* Reduced time and complexity of creating primary
products
* Intrinsic compatibility with digital technologies

31
Q

why can we not measure an oblique photo

A

because stuff in the foreground middleground and background are all different sizes and distances away because of the angle at which the photo is taken.

32
Q

what are the types of aerial photography and do all images have tilt>?

A
  • Type of aerial photos
    – Vertical
    – Oblique
  • All images are tilted, even the vertical ones
33
Q

what is the nadir line

A

Nadir line - line on the ground directly
beneath the aircraft during photo acquisition

34
Q

what is the zenith line

A

zenith is the line that points up from the earths sufrace while nadir points down

35
Q

what is Stereopsis

A
  • Stereopsis - the perception of depth and 3D obtained from visual information of two eyes
  • Forward Overlapping with more than 50%
    essential for stereoscopic coverage-usually 60%
  • Air base – ground distance between centers of two successive photo
  • Side overlap of ≈30%
36
Q

what is a photoscale

A

Photograph scale: one unit of distance on the photo represents a specific number of units in reality

37
Q

what are the two types of displacement

A
  1. Tilt displacement
    * Caused by a tilt of the image
  2. Terrain displacement
    * Caused by terrain morphology
38
Q

what is tilt displacement

A

Tilt displacement - the shift
in an object’s image position
on a tilted photo from its
position on a vertical photo.

39
Q

what is relief displacement

A

Relief displacement - the
shift in an object’s image
position caused by its
elevation above datum.

remote sensing (4 decks)

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